The　activity　of　photocatalytic　CO2　reduction　(PCR)　remains　inadequate　due　to　the　thermodynamically　stable　CO2　molecules　and　sluggish　carrier　kinetics.　This　work　simultaneously　adopts　active　site　and　heterojunction　engineering　to　collaboratively　enhance　PCR.　A　heterojunction　of　g-C3N4　microtube-supported　Co3O4　nanoparticle　has　been　developed　through　the　hydrothermal　pretreatment　and　calcination　processes.　The　g-C3N4　microtubes　play　dual　roles　in　enhancing　PCR　of　Co3O4:　(1)　they　act　as　a　substrate　to　support　Co3O4　nanoparticles,　thereby　making　small　size　and　good　dispersion　of　Co3O4　nanoparticles.　The　Co　active　sites　can　be　highly　exposed　to　accept　photogenerated　electrons　and　capture　CO2　molecules;　and　(2)　the　p-type　Co3O4　nanoparticles　and　n-type　g-C3N4　microtubes　build　a　p-n　junction.　An　internal　electric　field　is　created　to　expedite　the　charge　transfer.　As　a　result,　the　g-C3N4　microtube-supported　Co3O4　nanoparticle　affords　a　significantly　high　turnover　number　(TON)　of　24.72,　which　is　24-fold　higher　than　that　of　the　pure　Co3O4　and　comparable　to　state-of-the-art　photocatalysts.